452 4.5.3 Too many recipients
You tried to address one message to more recipients than the server accepts in a single transaction. The server accepts the recipients up to its limit and refuses the rest with 452; a correct MTA then delivers to the accepted ones and sends the remainder in a new transaction. Where you see this as a bounce, the client did not handle the partial acceptance.
What the server replies
452 4.5.3 Error: too many recipients
- Sent by
- Any mail server
- Type
- TemporaryRetry helps
- About
- Rate limits and quotas
- Enhanced code
- 4.5.3
Who sends it
Postfix enforces smtpd_recipient_limit (default 1000) and returns exactly this text; Exchange Online limits a message to 500 recipients; Gmail SMTP accepts 100 per message; many providers set lower per-message limits on authenticated submission.
Why it happens
- A script builds one message with the whole mailing list in To, Cc or Bcc.
- A distribution group expanded to more addresses than the next hop allows.
- A client library that puts every address into one SMTP transaction with no splitting.
- A receiver that deliberately sets a low limit to discourage bulk mail.
How to fix it
Split the recipients
Send in batches below the lowest limit you expect to meet; 50 per message is safe almost everywhere. Most libraries can do this for you.
Send one message per recipient for bulk mail
For newsletters and notifications, one message per person is the norm. It also lets you personalise and track bounces per address.
Admin: raise the limit if you own the server
On Postfix, smtpd_recipient_limit can be raised for an internal relay. Do not raise it on a server that receives from the internet.
Check it yourself
These free tools show the records and connections behind this code for your own domain or server.
Related codes
- 550 5.4.5 Daily sending quota exceededThis one comes back when you send through Gmail, not to it.
- 454 Throttling failure: Maximum sending rate exceededYour application is submitting to SES faster than the account's per-second sending rate, or has used its 24-hour quota (the wording is then "Daily message quota exceeded").
- 552 5.3.4 Message size exceeds fixed maximum message sizeThe message is larger than the receiving server allows.
Sources
Fewer bounces to look up.
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